Heat dissipation system

ABSTRACT

A system for dissipating heat generated by an electronic system, for example an electronic device in an aircraft. The system includes a housing including an external lid covering the electronic system and configured to be in contact with a first cold source, and a second cold source located inside the external lid. The housing includes an internal lid located inside the external lid and covering the electronic system, the second cold source being located between the internal and external lids.

This invention relates to a heat dissipation system.

It applies especially to a system for dissipation of the heat produced by an electronic system, in particular by an electronic equipment item in an aircraft.

Electronic systems heat up during their operation. The reliability and the quality of electronic systems are highly dependent on the temperature to which they are subjected. In fact, if the electronic systems are subjected to excessively high temperatures, they may exhibit failures.

The heat produced by the operation of an electronic system therefore must be dissipated and directed toward a cold source. In order to facilitate that, the thermal resistance between the system and the cold source must be reduced to the minimum.

Nonetheless, if the temperature of the cold source varies markedly, the temperature of the electronic system undergoes temperature changes.

The reliability of electronic systems that are subjected to great temperature variations is considerably reduced and their aging is accelerated.

Furthermore, in an aircraft, it is advantageous to position certain electronic equipment items outside protected zones of the aircraft. The thermal conditions in these unprotected zones are close to conditions outside the aircraft.

For example, unprotected zones are the tail cone or the interior of the wing group of the aircraft.

In this way, electronic equipment items are subjected to environmental stresses, and in particular to extreme thermal conditions.

Consequently, the reliability of such electronic equipment items is reduced and their aging accelerated.

There thus is known in document EP 1 615 488 a printed circuit accommodated in a housing and in contact with an interface layer forming a heat sink. Such a heat dissipation system, however, is limited to the use of a cold source in contact with the electronic system.

This invention has as a purpose to propose a heat dissipation system making it possible at the same time to reduce the effect of thermal variations of the cold source on the electronic equipment in an aircraft.

To this end, this invention relates according to a first aspect to a system for dissipation of the heat produced by an electronic system, in particular by an electronic equipment item in an aircraft, the dissipation system comprising a housing that includes an external lid covering the electronic system and adapted for being in contact with a first cold source, and a second cold source located inside the external lid.

According to the invention, the housing comprises an internal lid located inside the external lid and covering the electronic system, the second cold source being located between the internal and external lids.

In this way, the housing and the second cold source (which are disposed between the electronic system and the first cold source) mitigate the effect of the temperature variations of the first cold source on the electronic system. Consequently, the electronic system only slightly undergoes the temperatures variations of the first cold source, while allowing dissipation of the heat produced by the electronic system.

Furthermore, the internal lid protects the electronic system from contact with the second cold source.

According to a preferred characteristic, the internal lid and the external lid form a cavity containing the second cold source.

In this way, the electronic system is surrounded by the second cold source, and consequently insulated from the first cold source. The effect of temperature changes of the first cold source on the electronic system thus is minimized.

Consequently, if for example, the first cold source is the ambient air, the heat produced by the electronic equipment in an aircraft is directed toward the ambient air, and at the same time the electronic system is insulated from the ambient air and less exposed to the stresses of the environment.

Moreover, the electronic equipment only slightly undergoes the temperature changes of the environment.

In fact, it is necessary to extract the heat dissipated by the electronic equipment and at the same time to protect the electronic equipment from the effect of extreme thermal conditions.

According to one embodiment, the second cold source has a heat capacity value greater than the heat capacity value of the first cold source.

In this way, the second cold source absorbs the temperature variations of the first cold source and the electronic system only slightly undergoes the temperature variations of the first cold source, while allowing dissipation of the heat produced by the electronic system.

The second cold source advantageously comprises water.

By virtue of the significant heat capacity of the water, the temperature changes of the ambient air are tempered by the water.

In practice, the housing comprises six faces, a first face being fastened to a support and the other five faces being adapted for being in contact with the first cold source.

In this way, the surface of the housing through which the heat produced by the electronic system is transmitted toward the first cold source is maximized.

According to a second aspect, the invention applies to an aircraft comprising a dissipation system according to the invention.

Consequently, when the dissipation system according to the invention is used in order to dissipate the heat produced by an electronic equipment item located in a non-pressurized zone of an aircraft, the reliability and service life of the electronic equipment are increased.

This aircraft has characteristics and advantages similar to those described above in relation to the dissipation system.

Other features and advantages also will become apparent in the description below.

In the attached drawings, provided by way of non-limitative examples:

FIG. 1 is a diagram illustrating a longitudinal section of a dissipation system according to an embodiment of the invention;

FIG. 2 a shows the evolution of the temperature of a first cold source in time;

FIG. 2 b shows the evolution of the temperature of a second cold source in time; and

FIG. 2 c shows the evolution of the temperature of an electronic system in time.

A dissipation system according to an embodiment of the invention first is going to be described with reference to FIG. 1.

An electronic board 1 comprising an electronic system is fastened on a support or rack 2.

A lid 3 also is fastened to rack 2, forming therewith a housing 4. In this way, this housing 4 encloses and protects the outside of the electronic board 1.

In this way, the dimensions of housing 4 are according to the dimensions of electronic board 1.

In this example, housing 4 has a parallelepiped shape.

By way of example in no way limitative, the length and the width of the housing may be in a range from 200 to 500 mm and the height may be in a range from 20 to 300 mm.

The housing, for example, may be made of aluminum or of composite materials.

Of course, the dimensions and materials in which the housings are constructed may be different.

Here, the outside of housing 4 is in contact with ambient air 5, which represents a first cold source 5.

In fact, the heat produced by electronic board 1 is directed toward cold source 5, that is to say toward ambient air 5, through housing 4.

Housing 4 comprises an internal lid 8 located inside external lid 3 and covering electronic system 1 (here, electronic board 1).

In this way, internal lid 8 is disposed between electronic board 1 and external lid 3.

Lids 3, 8 form between them a cavity 6. This cavity 6 comprises a material that constitutes a second cold source 6 a.

The heat capacity of second cold source 6 a is of a value greater than that of first cold source 5, that is to say that the second cold source requires a thermal energy supply greater than the first cold source in order to undergo a temperature increase.

Here, the material making up second cold source 6 a is mainly water, such as for example propylene glycol-water.

In this embodiment, for an electronic equipment item or system 1 occupying a volume of 800 ml (volume equivalent to a rise in the water level generated by the immersion of the electronic equipment or system 1 in a tank filled with water), the volume of water inside the cavity 6 is 330 ml.

Internal lid 8 protects electronic board 1 from contact with the material making up second cold source 6 a, here water.

Of course, the volume may have different values.

Furthermore, other materials with high heat capacity value may be used, such as, for example, Galden® (marketed by SOLVAY) or methoxy-nanofluorobutane.

The heat capacity (Cth) of the materials is calculated by means of the following formula known to the individual skilled in the art:

Cth=p×Cp×V

in which p is the density of the material, Cp is the mass heat capacity of the material and V the volume of material used.

In this way, for example, the heat capacity per unit volume of the air, the water and the aluminum has the following values:

Cth _(air)=1.2 kg/m³×1,407 J/(kg.K)×V=1,688 J/m³ ×V

Cth _(water)=1,000 kg/m³×4,180 J/(kg.K)×V=4,180,000 J/m³ ×V

Cth _(al)=2,800 kg/m³×910 J/(kg.K)×V=2,548,000 J/m³ ×V

Housing 4 is fastened by one of these faces 4 a to a support 7, the five other remaining faces being in contact with first cold source 5.

In this way, the five faces in contact with first cold source 5 (here, the ambient air) make it possible to exchange the heat dissipated by electronic board 1 with ambient air 5 by natural convection.

It will be noted that the size and the material in which housing 4 is constructed have an impact on the heat exchange capacity between second cold source 6 a and housing 4 and between housing 4 and first cold source 5.

In other embodiments, housing 4 may be adapted for increasing (or for decreasing) its heat exchange capacity with ambient air 5, for example by increasing (or by decreasing) the surface of housing 4 in contact with ambient air 5 or by modifying the material in which housing 4 is made up.

One way to increase the surface of housing 4 in contact with ambient air 5, without, for all that, increasing the volume of housing 4, is to add blades.

Of course, other means of heat exchange may be used, for example forced convection.

In fact, there are temperature exchanges between electronic board 1 and water 6 a, and between water 6 a and ambient air 5 (through the housing) instead of exchanges between electronic board 1 and ambient air 5 directly.

By virtue of the high heat capacity value of second cold source 6 a, electronic board 1 undergoes the temperature variations of ambient air 5 to a lesser extent. In fact, the temperature changes of ambient air 5 are mitigated by water 6 a.

As may be seen on FIG. 2 a, the temperature of ambient air 5 surrounding an aircraft may vary very considerably, and for example it may vary between −55° and 80° C. FIG. 2 a shows a variation of the temperature of ambient air 5 outside the aircraft in time. The temperature changes are cyclic, corresponding, for example, to flight frequency.

On FIG. 2 b, it may be seen that the temperature of second cold source 6 a absorbs these changes in temperature, the latter varying between −35° and 20° C. As for FIG. 2 a, the temperature variation is expressed according to time.

Thus, by virtue of the presence of second cold source 6 a with high heat exchange value, disposed between first cold source 5 and electronic board 1, the temperature of electronic board 1 also varies between −35° and 20° C., as can be seen on FIG. 2 c. As for FIGS. 2 a and 2 b, the temperature variation is expressed according to time.

In this way, by virtue of the invention, it is possible to increase the reliability and the service life of the electronic equipment items of an aircraft which are located in unprotected zones of the aircraft, the equipment items thus being exposed to considerable temperature variations.

Of course, many modifications may be made to the exemplary implementations described above without departing from the context of the invention.

For example, the materials used as second cold source may be varied.

Furthermore, the housing may comprise a different number of lids, and may have varied shapes. 

1-6. (canceled)
 7. A system for dissipation of heat produced by an electronic system, or by an electronic equipment item in an aircraft, comprising: a housing that includes an external lid covering the electronic system and configured to be in contact with a first cold source, and a second cold source located inside the external lid, wherein the housing further includes an internal lid located inside the external lid and covering the electronic system, the second cold source being located between the internal and external lids.
 8. A dissipation system according to claim 7, wherein the internal lid and the external lid form a cavity containing the second cold source.
 9. A dissipation system according to claim 7, wherein the second cold source has a heat capacity value greater than a heat capacity value of the first cold source.
 10. A dissipation system according to claim 7, wherein the housing comprises six faces, a first face being fastened to a support and the other five faces being configured to be in contact with the first cold source.
 11. A dissipation system according to claim 7, wherein the second cold source comprises water.
 12. An aircraft, comprising: a dissipation system according to claim
 7. 